Current-in-plane spin-valve (CIP-SV) magnetic sensors have been used as read sensors in magnetic disc drives. It has been predicted that the current-in-plane spin-valve (CIP-SV) will not be able to be used in discs having data densities beyond ˜100 Gbpsi. Other read sensor alternatives such as tunneling magnetoresistance sensors and current-perpendicular-to-plane (CPP) giant magnetoresistance sensors are being explored to replace the CIP-SV. There are issues with both of these types of sensors that are delaying them from being incorporated into products. Because of the vast amount of experience with CIP sensors, it would be advantageous to be able to use the CIP sensor in disc drives having data densities beyond 100 Gbpsi.
A general rule of thumb equation that gives the output voltage for a read sensor is ΔV=Ib*DRsheet(width/length)*ε, where Ib is the bias current, DRsheet is the maximum change in the sheet resistance of the sensor, width and length are the width and length of the sensor, and ε is an efficiency factor that takes into account things such as the sensitivity lost when patterning the sheet film into a final read head structure. For the CIP-SV, the DRsheet has reached its maximum around 3 to 4 Ω/square. The maximum Ib is limited by such things as Joule heating and asymmetry induced by the self fields from the bias current.
Spin valves include two layers of ferromagnetic material separated by a non-magnetic (NM) spacer layer. The direction of magnetization of one of the layers of ferromagnetic (FM) material, called the free layer, can be changed by interacting with an external magnetic field. The direction of magnetization of the other layer of ferromagnetic material, called the pinned layer, is fixed. Antiferromagnetic (AFM) material is needed in the CIP-SV to pin the pinned layer so that both an AFM and FM state can be achieved between the pinned and free layers when reading bits from the media.
This invention seeks to overcome the limitations spin valve CIP sensors by providing a CIP sensor that can produce a larger output from a smaller sensor, and does not require a pinning layer.